varying float u_op;
uniform float u_time;
uniform float u_height;
void main() {
    vec3 new_position = position * mod(u_time, 1.0);
    u_op =mix( 0.6,0.0,position.y / u_height) ;
    gl_Position = projectionMatrix * modelViewMatrix * vec4(new_position, 1.0);
}